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Serialize ZTHR operations to eliminate races

Browse Source 
Adds a new lock for serializing operations on zthrs.
The commit also includes some code cleanup and
refactoring.

Reviewed by: Matt Ahrens <mahrens@delphix.com>
Reviewed by: Tom Caputi <tcaputi@datto.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Serapheim Dimitropoulos <serapheim@delphix.com>
Closes #8229
This commit is contained in:
Serapheim Dimitropoulos 2019-01-13 10:09:46 -08:00 committed by Brian Behlendorf
parent 83c796c5e9
commit 61c3391acc
7 changed files with 192 additions and 130 deletions
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2
include/sys/spa_checkpoint.h
View File

@ -37,7 +37,7 @@ int spa_checkpoint(const char *);
int spa_checkpoint_discard(const char *);
boolean_t spa_checkpoint_discard_thread_check(void *, zthr_t *);
int spa_checkpoint_discard_thread(void *, zthr_t *);
void spa_checkpoint_discard_thread(void *, zthr_t *);
int spa_checkpoint_get_stats(spa_t *, pool_checkpoint_stat_t *);

22
include/sys/zthr.h
View File

@ -14,42 +14,26 @@
*/
/*
* Copyright (c) 2017 by Delphix. All rights reserved.
* Copyright (c) 2017, 2018 by Delphix. All rights reserved.
*/
#ifndef _SYS_ZTHR_H
#define _SYS_ZTHR_H
typedef struct zthr zthr_t;
typedef int (zthr_func_t)(void *, zthr_t *);
typedef void (zthr_func_t)(void *, zthr_t *);
typedef boolean_t (zthr_checkfunc_t)(void *, zthr_t *);
struct zthr {
kthread_t *zthr_thread;
kmutex_t zthr_lock;
kcondvar_t zthr_cv;
boolean_t zthr_cancel;
hrtime_t zthr_wait_time;
zthr_checkfunc_t *zthr_checkfunc;
zthr_func_t *zthr_func;
void *zthr_arg;
int zthr_rc;
};
extern zthr_t *zthr_create(zthr_checkfunc_t checkfunc,
zthr_func_t *func, void *arg);
extern zthr_t *zthr_create_timer(zthr_checkfunc_t *checkfunc,
zthr_func_t *func, void *arg, hrtime_t nano_wait);
extern void zthr_exit(zthr_t *t, int rc);
extern void zthr_destroy(zthr_t *t);
extern void zthr_wakeup(zthr_t *t);
extern int zthr_cancel(zthr_t *t);
extern void zthr_cancel(zthr_t *t);
extern void zthr_resume(zthr_t *t);
extern boolean_t zthr_iscancelled(zthr_t *t);
extern boolean_t zthr_isrunning(zthr_t *t);
#endif /* _SYS_ZTHR_H */

8
module/zfs/arc.c
View File

@ -5113,7 +5113,7 @@ arc_adjust_cb_check(void *arg, zthr_t *zthr)
* from the ARC.
*/
/* ARGSUSED */
static int
static void
arc_adjust_cb(void *arg, zthr_t *zthr)
{
uint64_t evicted = 0;
@ -5147,8 +5147,6 @@ arc_adjust_cb(void *arg, zthr_t *zthr)
}
mutex_exit(&arc_adjust_lock);
spl_fstrans_unmark(cookie);
return (0);
}
/* ARGSUSED */
@ -5190,7 +5188,7 @@ arc_reap_cb_check(void *arg, zthr_t *zthr)
* to free more buffers.
*/
/* ARGSUSED */
static int
static void
arc_reap_cb(void *arg, zthr_t *zthr)
{
int64_t free_memory;
@ -5231,8 +5229,6 @@ arc_reap_cb(void *arg, zthr_t *zthr)
arc_reduce_target_size(to_free);
}
spl_fstrans_unmark(cookie);
return (0);
}
#ifdef _KERNEL

14
module/zfs/spa.c
View File

@ -1486,13 +1486,11 @@ spa_unload(spa_t *spa)
}
if (spa->spa_condense_zthr != NULL) {
ASSERT(!zthr_isrunning(spa->spa_condense_zthr));
zthr_destroy(spa->spa_condense_zthr);
spa->spa_condense_zthr = NULL;
}
if (spa->spa_checkpoint_discard_zthr != NULL) {
ASSERT(!zthr_isrunning(spa->spa_checkpoint_discard_zthr));
zthr_destroy(spa->spa_checkpoint_discard_zthr);
spa->spa_checkpoint_discard_zthr = NULL;
}
@ -7214,12 +7212,12 @@ spa_async_suspend(spa_t *spa)
spa_vdev_remove_suspend(spa);
zthr_t *condense_thread = spa->spa_condense_zthr;
if (condense_thread != NULL && zthr_isrunning(condense_thread))
VERIFY0(zthr_cancel(condense_thread));
if (condense_thread != NULL)
zthr_cancel(condense_thread);
zthr_t *discard_thread = spa->spa_checkpoint_discard_zthr;
if (discard_thread != NULL && zthr_isrunning(discard_thread))
VERIFY0(zthr_cancel(discard_thread));
if (discard_thread != NULL)
zthr_cancel(discard_thread);
}
void
@ -7232,11 +7230,11 @@ spa_async_resume(spa_t *spa)
spa_restart_removal(spa);
zthr_t *condense_thread = spa->spa_condense_zthr;
if (condense_thread != NULL && !zthr_isrunning(condense_thread))
if (condense_thread != NULL)
zthr_resume(condense_thread);
zthr_t *discard_thread = spa->spa_checkpoint_discard_zthr;
if (discard_thread != NULL && !zthr_isrunning(discard_thread))
if (discard_thread != NULL)
zthr_resume(discard_thread);
}

6
module/zfs/spa_checkpoint.c
View File

@ -393,7 +393,7 @@ spa_checkpoint_discard_thread_check(void *arg, zthr_t *zthr)
return (B_TRUE);
}
int
void
spa_checkpoint_discard_thread(void *arg, zthr_t *zthr)
{
spa_t *spa = arg;
@ -408,7 +408,7 @@ spa_checkpoint_discard_thread(void *arg, zthr_t *zthr)
dmu_buf_t **dbp;
if (zthr_iscancelled(zthr))
return (0);
return;
ASSERT3P(vd->vdev_ops, !=, &vdev_indirect_ops);
@ -445,8 +445,6 @@ spa_checkpoint_discard_thread(void *arg, zthr_t *zthr)
VERIFY0(dsl_sync_task(spa->spa_name, NULL,
spa_checkpoint_discard_complete_sync, spa,
0, ZFS_SPACE_CHECK_NONE));
return (0);
}

6
module/zfs/vdev_indirect.c
View File

@ -647,7 +647,7 @@ spa_condense_indirect_thread_check(void *arg, zthr_t *zthr)
}
/* ARGSUSED */
static int
static void
spa_condense_indirect_thread(void *arg, zthr_t *zthr)
{
spa_t *spa = arg;
@ -744,13 +744,11 @@ spa_condense_indirect_thread(void *arg, zthr_t *zthr)
* shutting down.
*/
if (zthr_iscancelled(zthr))
return (0);
return;
VERIFY0(dsl_sync_task(spa_name(spa), NULL,
spa_condense_indirect_complete_sync, sci, 0,
ZFS_SPACE_CHECK_EXTRA_RESERVED));
return (0);
}
/*

254
module/zfs/zthr.c
View File

@ -14,7 +14,7 @@
*/
/*
* Copyright (c) 2017 by Delphix. All rights reserved.
* Copyright (c) 2017, 2019 by Delphix. All rights reserved.
*/
/*
@ -28,7 +28,7 @@
*
* 1] The operation needs to run over multiple txgs.
* 2] There is be a single point of reference in memory or on disk that
* indicates whether the operation should run/is running or is
* indicates whether the operation should run/is running or has
* stopped.
*
* If the operation satisfies the above then the following rules guarantee
@ -51,6 +51,9 @@
* during creation to wakeup on its own after a specified interval
* [see zthr_create_timer()].
*
* Note: ZTHR threads are NOT a replacement for generic threads! Please
* ensure that they fit your use-case well before using them.
*
* == ZTHR creation
*
* Every zthr needs three inputs to start running:
@ -64,17 +67,17 @@
* 2] A user-defined ZTHR function (func) which the zthr executes when
* it is not sleeping. The function should adhere to the following
* signature type:
* int func_name(void *args, zthr_t *t);
* void func_name(void *args, zthr_t *t);
*
* 3] A void args pointer that will be passed to checkfunc and func
* implicitly by the infrastructure.
*
* The reason why the above API needs two different functions,
* instead of one that both checks and does the work, has to do with
* the zthr's internal lock (zthr_lock) and the allowed cancellation
* windows. We want to hold the zthr_lock while running checkfunc
* but not while running func. This way the zthr can be cancelled
* while doing work and not while checking for work.
* the zthr's internal state lock (zthr_state_lock) and the allowed
* cancellation windows. We want to hold the zthr_state_lock while
* running checkfunc but not while running func. This way the zthr
* can be cancelled while doing work and not while checking for work.
*
* To start a zthr:
* zthr_t *zthr_pointer = zthr_create(checkfunc, func, args);
@ -83,7 +86,7 @@
* args, max_sleep);
*
* After that you should be able to wakeup, cancel, and resume the
* zthr from another thread using zthr_pointer.
* zthr from another thread using the zthr_pointer.
*
* NOTE: ZTHR threads could potentially wake up spuriously and the
* user should take this into account when writing a checkfunc.
@ -102,8 +105,8 @@
* zthr_resume(zthr_pointer);
*
* A zthr will implicitly check if it has received a cancellation
* signal every time func returns and everytime it wakes up [see ZTHR
* state transitions below].
* signal every time func returns and every time it wakes up [see
* ZTHR state transitions below].
*
* At times, waiting for the zthr's func to finish its job may take
* time. This may be very time-consuming for some operations that
@ -119,17 +122,8 @@
* while (!work_done && !zthr_iscancelled(t)) {
* ... <do more work> ...
* }
* return (0);
* }
*
* == ZTHR exit
*
* For the rare cases where the zthr wants to stop running voluntarily
* while running its ZTHR function (func), we provide zthr_exit().
* When a zthr has voluntarily stopped running, it can be resumed with
* zthr_resume(), just like it would if it was cancelled by some other
* thread.
*
* == ZTHR cleanup
*
* Cancelling a zthr doesn't clean up its metadata (internal locks,
@ -165,49 +159,86 @@
* v
* zthr stopped running
*
* == Implementation of ZTHR requests
*
* ZTHR wakeup, cancel, and resume are requests on a zthr to
* change its internal state. Requests on a zthr are serialized
* using the zthr_request_lock, while changes in its internal
* state are protected by the zthr_state_lock. A request will
* first acquire the zthr_request_lock and then immediately
* acquire the zthr_state_lock. We do this so that incoming
* requests are serialized using the request lock, while still
* allowing us to use the state lock for thread communication
* via zthr_cv.
*/
#include <sys/zfs_context.h>
#include <sys/zthr.h>
void
zthr_exit(zthr_t *t, int rc)
{
ASSERT3P(t->zthr_thread, ==, curthread);
mutex_enter(&t->zthr_lock);
t->zthr_thread = NULL;
t->zthr_rc = rc;
cv_broadcast(&t->zthr_cv);
mutex_exit(&t->zthr_lock);
thread_exit();
}
struct zthr {
/* running thread doing the work */
kthread_t *zthr_thread;
/* lock protecting internal data & invariants */
kmutex_t zthr_state_lock;
/* mutex that serializes external requests */
kmutex_t zthr_request_lock;
/* notification mechanism for requests */
kcondvar_t zthr_cv;
/* flag set to true if we are canceling the zthr */
boolean_t zthr_cancel;
/*
* maximum amount of time that the zthr is spent sleeping;
* if this is 0, the thread doesn't wake up until it gets
* signaled.
*/
hrtime_t zthr_wait_time;
/* consumer-provided callbacks & data */
zthr_checkfunc_t *zthr_checkfunc;
zthr_func_t *zthr_func;
void *zthr_arg;
};
static void
zthr_procedure(void *arg)
{
zthr_t *t = arg;
int rc = 0;
mutex_enter(&t->zthr_lock);
mutex_enter(&t->zthr_state_lock);
ASSERT3P(t->zthr_thread, ==, curthread);
while (!t->zthr_cancel) {
if (t->zthr_checkfunc(t->zthr_arg, t)) {
mutex_exit(&t->zthr_lock);
rc = t->zthr_func(t->zthr_arg, t);
mutex_enter(&t->zthr_lock);
mutex_exit(&t->zthr_state_lock);
t->zthr_func(t->zthr_arg, t);
mutex_enter(&t->zthr_state_lock);
} else {
/* go to sleep */
if (t->zthr_wait_time == 0) {
cv_wait_sig(&t->zthr_cv, &t->zthr_lock);
cv_wait_sig(&t->zthr_cv, &t->zthr_state_lock);
} else {
(void) cv_timedwait_sig_hires(&t->zthr_cv,
&t->zthr_lock, t->zthr_wait_time,
&t->zthr_state_lock, t->zthr_wait_time,
MSEC2NSEC(1), 0);
}
}
}
mutex_exit(&t->zthr_lock);
zthr_exit(t, rc);
/*
* Clear out the kernel thread metadata and notify the
* zthr_cancel() thread that we've stopped running.
*/
t->zthr_thread = NULL;
t->zthr_cancel = B_FALSE;
cv_broadcast(&t->zthr_cv);
mutex_exit(&t->zthr_state_lock);
thread_exit();
}
zthr_t *
@ -226,10 +257,11 @@ zthr_create_timer(zthr_checkfunc_t *checkfunc, zthr_func_t *func,
void *arg, hrtime_t max_sleep)
{
zthr_t *t = kmem_zalloc(sizeof (*t), KM_SLEEP);
mutex_init(&t->zthr_lock, NULL, MUTEX_DEFAULT, NULL);
mutex_init(&t->zthr_state_lock, NULL, MUTEX_DEFAULT, NULL);
mutex_init(&t->zthr_request_lock, NULL, MUTEX_DEFAULT, NULL);
cv_init(&t->zthr_cv, NULL, CV_DEFAULT, NULL);
mutex_enter(&t->zthr_lock);
mutex_enter(&t->zthr_state_lock);
t->zthr_checkfunc = checkfunc;
t->zthr_func = func;
t->zthr_arg = arg;
@ -237,7 +269,7 @@ zthr_create_timer(zthr_checkfunc_t *checkfunc, zthr_func_t *func,
t->zthr_thread = thread_create(NULL, 0, zthr_procedure, t,
0, &p0, TS_RUN, minclsyspri);
mutex_exit(&t->zthr_lock);
mutex_exit(&t->zthr_state_lock);
return (t);
}
@ -245,71 +277,130 @@ zthr_create_timer(zthr_checkfunc_t *checkfunc, zthr_func_t *func,
void
zthr_destroy(zthr_t *t)
{
ASSERT(!MUTEX_HELD(&t->zthr_state_lock));
ASSERT(!MUTEX_HELD(&t->zthr_request_lock));
VERIFY3P(t->zthr_thread, ==, NULL);
mutex_destroy(&t->zthr_lock);
mutex_destroy(&t->zthr_request_lock);
mutex_destroy(&t->zthr_state_lock);
cv_destroy(&t->zthr_cv);
kmem_free(t, sizeof (*t));
}
/*
* Note: If the zthr is not sleeping and misses the wakeup
* (e.g it is running its ZTHR function), it will check if
* there is work to do before going to sleep using its checker
* function [see ZTHR state transition in ZTHR block comment].
* Thus, missing the wakeup still yields the expected behavior.
* Wake up the zthr if it is sleeping. If the thread has been
* cancelled that does nothing.
*/
void
zthr_wakeup(zthr_t *t)
{
mutex_enter(&t->zthr_lock);
mutex_enter(&t->zthr_request_lock);
mutex_enter(&t->zthr_state_lock);
/*
* There are 4 states that we can find the zthr when issuing
* this broadcast:
*
* [1] The common case of the thread being asleep, at which
* point the broadcast will wake it up.
* [2] The thread has been cancelled. Waking up a cancelled
* thread is a no-op. Any work that is still left to be
* done should be handled the next time the thread is
* resumed.
* [3] The thread is doing work and is already up, so this
* is basically a no-op.
* [4] The thread was just created/resumed, in which case the
* behavior is similar to [3].
*/
cv_broadcast(&t->zthr_cv);
mutex_exit(&t->zthr_lock);
mutex_exit(&t->zthr_state_lock);
mutex_exit(&t->zthr_request_lock);
}
/*
* Note: If the zthr is not running (e.g. has been cancelled
* Sends a cancel request to the zthr and blocks until the zthr is
* cancelled. If the zthr is not running (e.g. has been cancelled
* already), this is a no-op.
*/
int
void
zthr_cancel(zthr_t *t)
{
int rc = 0;
mutex_enter(&t->zthr_request_lock);
mutex_enter(&t->zthr_state_lock);
mutex_enter(&t->zthr_lock);
/*
* Since we are holding the zthr_state_lock at this point
* we can find the state in one of the following 4 states:
*
* [1] The thread has already been cancelled, therefore
* there is nothing for us to do.
* [2] The thread is sleeping, so we broadcast the CV first
* to wake it up and then we set the flag and we are
* waiting for it to exit.
* [3] The thread is doing work, in which case we just set
* the flag and wait for it to finish.
* [4] The thread was just created/resumed, in which case
* the behavior is similar to [3].
*
* Since requests are serialized, by the time that we get
* control back we expect that the zthr is cancelled and
* not running anymore.
*/
if (t->zthr_thread != NULL) {
t->zthr_cancel = B_TRUE;
/* broadcast in case the zthr is sleeping */
cv_broadcast(&t->zthr_cv);
t->zthr_cancel = B_TRUE;
while (t->zthr_thread != NULL)
cv_wait(&t->zthr_cv, &t->zthr_lock);
t->zthr_cancel = B_FALSE;
rc = t->zthr_rc;
mutex_exit(&t->zthr_lock);
cv_wait(&t->zthr_cv, &t->zthr_state_lock);
return (rc);
ASSERT(!t->zthr_cancel);
}
mutex_exit(&t->zthr_state_lock);
mutex_exit(&t->zthr_request_lock);
}
/*
* Sends a resume request to the supplied zthr. If the zthr is
* already running this is a no-op.
*/
void
zthr_resume(zthr_t *t)
{
ASSERT3P(t->zthr_thread, ==, NULL);
mutex_enter(&t->zthr_lock);
mutex_enter(&t->zthr_request_lock);
mutex_enter(&t->zthr_state_lock);
ASSERT3P(&t->zthr_checkfunc, !=, NULL);
ASSERT3P(&t->zthr_func, !=, NULL);
ASSERT(!t->zthr_cancel);
/*
* There are 4 states that we find the zthr in at this point
* given the locks that we hold:
*
* [1] The zthr was cancelled, so we spawn a new thread for
* the zthr (common case).
* [2] The zthr is running at which point this is a no-op.
* [3] The zthr is sleeping at which point this is a no-op.
* [4] The zthr was just spawned at which point this is a
* no-op.
*/
if (t->zthr_thread == NULL) {
t->zthr_thread = thread_create(NULL, 0, zthr_procedure, t,
0, &p0, TS_RUN, minclsyspri);
}
mutex_exit(&t->zthr_lock);
mutex_exit(&t->zthr_state_lock);
mutex_exit(&t->zthr_request_lock);
}
/*
* This function is intended to be used by the zthr itself
* to check if another thread has signal it to stop running.
* (specifically the zthr_func callback provided) to check
* if another thread has signaled it to stop running before
* doing some expensive operation.
*
* returns TRUE if we are in the middle of trying to cancel
* this thread.
@ -319,25 +410,22 @@ zthr_resume(zthr_t *t)
boolean_t
zthr_iscancelled(zthr_t *t)
{
boolean_t cancelled;
ASSERT3P(t->zthr_thread, ==, curthread);
mutex_enter(&t->zthr_lock);
cancelled = t->zthr_cancel;
mutex_exit(&t->zthr_lock);
/*
* The majority of the functions here grab zthr_request_lock
* first and then zthr_state_lock. This function only grabs
* the zthr_state_lock. That is because this function should
* only be called from the zthr_func to check if someone has
* issued a zthr_cancel() on the thread. If there is a zthr_cancel()
* happening concurrently, attempting to grab the request lock
* here would result in a deadlock.
*
* By grabbing only the zthr_state_lock this function is allowed
* to run concurrently with a zthr_cancel() request.
*/
mutex_enter(&t->zthr_state_lock);
boolean_t cancelled = t->zthr_cancel;
mutex_exit(&t->zthr_state_lock);
return (cancelled);
}
boolean_t
zthr_isrunning(zthr_t *t)
{
boolean_t running;
mutex_enter(&t->zthr_lock);
running = (t->zthr_thread != NULL);
mutex_exit(&t->zthr_lock);
return (running);
}